This application is a continuation of International Application No. PCT/JP00/01193, filed Mar. 1, 2000, which claims the benefit of Japanese Patent Application No. 11-053793, filed Mar. 2, 1999.
The invention disclosed in the present application relates to electron beam emitting apparatus and image-forming apparatus. More particularly, the invention concerns the electron beam emitting apparatus and image-forming apparatus provided with a lot of electron-emitting devices.
There are two types of electron-emitting devices known heretofore, thermionic emission sources and cold-cathode emission sources, and there are also the known image-forming apparatus making use of these electron sources.
The image-forming apparatus illustrated in FIG. 11 is known as a plane type image-forming apparatus using the thermionic emission source. FIG. 11 is a schematic structural diagram of the image-forming apparatus using the conventional thermionic emission source.
This image-forming apparatus has a plurality of anodes 1502, which are arranged in parallel on an insulating substrate 1501 and the surface of which is coated with a material that emits fluorescence upon collision of an electron beam therewith (phosphor), a plurality of filaments 1503, which are arranged in parallel and opposite to the anodes 1502, and a plurality of grid electrodes 1504, which are arranged perpendicular to the anodes 1502 and filaments 1503 between the anodes 1502 and the filaments 1503, and these anodes 1502, filaments 1503, and grid electrodes 1504 are held in a transparent vessel 1505. The vessel 1505 is hermetically bonded (hereinafter referred to as xe2x80x9csealedxe2x80x9d) to the insulating substrate 1501 so as to be able to keep the inside in vacuum, and the inside of the envelope constructed of the vessel 1505 and the insulating substrate 1501 is kept in the vacuum of about 1.3xc3x9710xe2x88x924 Pa.
The filaments 1503 emit electrons when heated in vacuum and, with application of respectively appropriate voltages to the grid electrodes 1504 and to the anodes 1502, the electrons emitted from the filaments 1503 collide with the anodes 1502, whereupon the phosphor on the anodes 1502 emits fluorescence. Light-emitting positions can be controlled by matrix addressing of the lines of anodes 1502 (in the X-direction) and the lines of grid electrodes 1504 (in the Y-direction), whereby an image can be displayed through the vessel 1505.
The image-forming apparatus using the thermionic emission source, however, has the following problems: (1) power consumption is large, (2) it is difficult to implement large-capacity display because of slow modulation speed, and (3) variation occurs readily among the devices, and it is not easy to realize a large screen, because the structure becomes complex. Thus there are also the image-forming apparatus using the cold-cathode emission source instead of the thermionic emission source.
The cold-cathode emission sources include field emission type (hereinafter referred to as xe2x80x9cFE typexe2x80x9d), metal/insulator/metal type (hereinafter referred to as xe2x80x9cMIM typexe2x80x9d), surface conduction electron-emitting devices, and so on.
Examples of the known FE type devices are those described in W. P. Dyke and W. W. Dolan, xe2x80x9cField emissionxe2x80x9d, Advance in Electron Physics, 8, 89 (1956), or in C. A. Spindt, xe2x80x9cPhysical Properties of thin-film field emission cathodes with molybdenum conesxe2x80x9d, J. Appl. Phys., 47, 5248, (1976), and so on.
An example of the image-forming apparatus using this FE type electron source will be described referring to FIG. 12. FIG. 12 is a schematic, structural diagram to show the conventional image-forming apparatus with the FE type electron source, partly enlarged.
As illustrated in FIG. 12, this image-forming apparatus has an electron source 2001, in which many electron-emitting devices are formed, and a face plate 2003 opposed to the electron source 2001. The electron source 2001 is comprised of a lot of micropoints 2013, which are formed in an electrically connected state through electric conductors 2012 on an insulating substrate 2011, and a grid 2015, which has apertures corresponding to the micropoints 2013 and which is supported on the insulating substrate 2011 while being electrically insulated from the micropoints 2013 by insulating layer 2014. The bottoms of the micropoints 2013 have the diameter and height of about 2 xcexcm and the diameter of the apertures in the grid 2015 is also about 2 xcexcm.
The face plate 2003 is comprised of the phosphor 2032, which is laid on the inner surface of glass sheet 2031, and an electroconductive film 2033, which covers the phosphor 2032 and which acts as an acceleration electrode to which a voltage for accelerating electrons emitted from the micropoints 2013 is applied.
In the above structure, the distance is very small between the tips of the micropoints 2013 and the grid 2015 (not more than 1 xcexcm), and the tips of the micropoints 2013 are of a pointed shape. Therefore, a strong electric field (not less than 107 V/cm) capable of field electron emission can be created between the micropoints 2013 and the grid 2015 even by the potential difference of not more than 100 V. The amount of electron emission from one micropoint 2013 is approximately several xcexcA. Since it is possible to form approximately several ten thousand micropoints 2013 per mm2, an electron-emitting device corresponding to one pixel is normally composed of a set of about several thousand to several ten thousand micropoints 2013 in the image-forming apparatus. Therefore, the electron emission amount can be over several mA per electron-emitting device corresponding to one pixel.
The potentials at the grid 2015 and at the micropoints 2013 are set, for example, as follows: the earth potential (0 V) is applied to the grid 2015 and a negative potential (about xe2x88x92100 V) is applied through the conductor 2012 to the micropoints 2013, which implements electron emission. Further, a potential equal to or greater than that at the grid 2015 is applied through the conductive film 2033 to the face plate 2003, whereby the electrons emitted from the electron source 2001 come to collide with the phosphor 2032 to excite the phosphor and effect light emission thereof.
For controlling luminous points of this emission, there are provided a plurality of row wires 2041 formed of an array of X-directional beltlike conductors 2012, each being electrically connected to a plurality of micropoints 2013, and column wires 2042 of the grid 2015 electrically connected in the Y-direction, and an image can be displayed in such a manner that matrix addressing is implemented so as to apply a voltage over a desired electron emission start voltage to desired areas out of a plurality of electron-emitting device areas 2010 formed at intersections of this matrix wire pattern from external power supplies 2043, 2044, thereby selecting positions where the electrons impinge upon the phosphor 2032 to which the voltage is applied through the conductive film 2033 from an acceleration voltage supply 2045.
On the other hand, examples of the known MIM devices are those described in C. A. Mead, xe2x80x9cOperation of Tunnel-emission Devicesxe2x80x9d, J. Appl. Phys., 32,646 (1961) and so on.
Examples of the surface conduction electron-emitting devices are those described in M. I. Elinson, Radio Eng. Electron Phys., 10, (1965) and so on.
The surface conduction electron-emitting devices are the electron-emitting devices making use of the phenomenon that electron emission occurs when electric current flows in parallel to the surface in small-area thin film formed on a substrate. The surface conduction electron-emitting devices reported heretofore include those using thin films of SnO2 reported by aforementioned Elinson et al., those using thin films of Au [G. Dittmer: xe2x80x9cThin Solid Films,xe2x80x9d 9,317 (1972)], those using thin films of In2O3/SnO2 [M. Hartwell and C. G. Fonstad: xe2x80x9cIEEE Trans. ED Conf.xe2x80x9d, 519 (1975)], those using thin films of carbon [Hisashi Araki et al.: Vacuum, vol 26, No. 1, p22 (1983)], and so on.
FIG. 13 is a plan view of the device reported by aforementioned M. Hartwell et al., which is a typical example of the device configuration of these surface conduction electron-emitting devices. In the same figure numeral 3001 designates a substrate and 3004 an electroconductive thin film made of a metallic oxide by sputtering. The conductive thin film 3004 is formed in a plane shape of H-pattern as illustrated. An electron-emitting region 3005 is made by an energization process called energization forming described hereinafter, in the conductive thin film 3004. In the figure the clearance L between the device electrodes is set to 0.5 to 1 mm and W to 0.1 mm. For convenience sake of illustration, the electron-emitting region 3005 is illustrated in the rectangular shape in the center of the conductive, thin film 3004, but this is just a schematic illustration, which does not always loyally represent the position and shape of the actual electron-emitting region.
In the above-stated surface conduction electron-emitting devices including the device by M. Hartwell et al., it was common practice to form the electron-emitting region 3005 by subjecting the conductive thin film 3004 to the energization process called energization forming before execution of electron emission. Namely, the energization forming is a process of placing a constant, direct current or a direct current with increasing voltage at a very slow rate, for example, of about 1 V/min between the both ends of the conductive thin film 3004 to energize it, so as to locally break or deform or modify the conductive thin film 3004, thereby forming the electron-emitting region 3005 in an electrically high resistance state.
A fissure is created in part of the locally broken or deformed or modified, conductive thin film 3004. When an appropriate voltage is applied to the conductive thin film 3004 after the energization forming, electron emission occurs near the fissure.
Since the cold-cathode emission sources described above can be made by the technology, for example, such as photolithography, etching, and the like, it is feasible to place many devices at small intervals. In addition, the cathodes and surroundings can be driven under relatively lower temperature conditions than in the case of the thermionic emission sources, and thus multiple electron beam emission sources can be readily realized at finer array pitch. Among these cold-cathode emission sources, the surface conduction electron-emitting devices are particularly suitable for the electron-emitting devices used in the large-screen image-forming apparatus desired recently, because they are advantageous in that the device structure is simple and easy to produce and in that it is easy to produce a large-area screen.
For example, a known image-forming apparatus using the electron-emitting devices of this type is constructed in such structure that an electron source with the electron-emitting devices formed therein is opposed through a support frame to an image-forming member equipped with the phosphor or the like emitting fluorescence upon collision of electrons therewith and that the inside of an envelope composed of these electron source, image-forming member, and support frame is kept in vacuum.
The image-forming member is provided with the acceleration electrode for accelerating the electrons emitted from the electron source toward the image-forming member, and the emitted electrons are accelerated toward the image-forming member with application of high voltage to the acceleration electrode, to collide with the image-forming member. Therefore, the support frame is made of an insulating material resistant to the high voltage.
An object of the invention in the present application is to realize suitable electron beam emitting apparatus.
One aspect of the invention of the electron beam emitting apparatus in the present application is configured as follows.
An electron beam emitting apparatus comprises a first plate in which an electron-emitting device is formed and an electrode opposed to the first plate, the electrode being applied a potential for accelerating electrons emitted from the electron-emitting device, the electron beam emitting apparatus being characterized in that a potential defining region is provided on a said-electrode-side surface of said first plate and a first potential defining region constituting said potential defining region is provided in a projective area of said electrode onto said potential defining region and in that, where d represents a distance between said electrode and said potential defining region, a marginal area to be potential-defined is defined in a range of 0.83d in all directions parallel to said first plate from the edge of the projective area of said electrode onto said potential defining region and an additional potential defining region is provided in almost all the marginal area to be potential-defined.
The potential defining region can be either of various configurations and desirably one with some electric conductivity capable of defining the potential. Specifically, the potential defining region is desirably one having the surface resistance of not more than 1xc3x971012 xcexa9/xe2x96xa1. It can also be contemplated that wiring having other function as well constitutes at least part of the potential defining region. For example, the wires connected to the electron-emitting device can also serve as the potential defining region. An electric conductor of film shape can also be provided as the potential defining region other than the wires. In this case there are various ways of defining the potential of the conductor of film shape, and a suitable configuration is such that the potential of the conductive film is defined by electrically connecting the conductive film to some wiring. The wiring can be the aforementioned wires connected to the electron-emitting device. When the conductive film forming the potential defining region is one with high resistance, it becomes feasible to provide the conductive film in contact with a plurality of wires connected to the electron-emitting device.
The first potential defining region and the additional potential defining region do not have to be separate members. Suitably applicable configurations include a configuration in which a certain member, e.g. a certain wire, serves as the first potential defining region in the first potential defining zone and as the additional potential defining region in the additional potential defining zone and a configuration in which a conductive film simultaneously formed in the first potential defining zone and in the additional potential defining zone serves as the first potential defining region in the first potential defining zone and as the additional potential defining region in the additional potential defining zone.
The potential defining region (the first potential defining region and the additional potential defining region) is exposed to an atmosphere (particularly, a reduced pressure or vacuum atmosphere) in the apparatus.
The phrase xe2x80x9cthe additional potential defining region is provided in almost all the marginal area to be potential-definedxe2x80x9d stated herein means that the additional potential defining region is provided in not less than 80% of the marginal area to be potential-defined. Insulating areas not potential-defined may exist in part in the marginal area to be potential-defined, but the rate thereof needs to be not more than 20% of the marginal area to be potential-defined. Further, where the insulating areas exist in the marginal area to be potential-defined, it is particularly preferable that the size of each insulating area be not more than 0.5dxc3x970.5d.
It is also desirable that the first potential defining region provided in the projective area of the electrode be provided in almost all the projective area. Specifically, the first potential defining region is preferably provided in the area not less than 80% in the projective area. Some areas can be insulating areas not potential-defined in the projective area, but the rate thereof needs to be not more than 20% of the projective area. Further, where the insulating areas exist in the projective area, it is particularly preferable that the size of each insulating area be not more than 0.5dxc3x970.5d.
Further preferably, it is desirable that the additional potential defining region be one specified in such a way that the marginal area to be potential-defined is set in a range of d in all the directions parallel to the first plate from the edge of the projective area of the electrode onto the potential defining region (the so-set marginal area being referred to hereinafter as an expanded marginal area to be potential-defined) and that the additional potential defining region is provided in almost all the marginal area to be potential-defined. In this case, the phrase xe2x80x9cthe additional potential defining region is provided in almost all the expanded marginal area to be potential-defined also means that the additional potential defining region is provided in the area not less than 80% of the expanded marginal area to be potential-defined. In the expanded marginal area to be potential-defined, the suitably permissible condition for insulating areas is the same as described above.
It is preferable that areas with the surface resistance of not more than 1xc3x97105 xcexa9/xe2x96xa1 exist 50% or more in the projective area and the marginal area to be potential-defined, or in the projective area and the expanded marginal area to be potential-defined. Particularly, it is preferable that areas with the surface resistance of not more than 1xc3x97105 xcexa9/xe2x96xa1 exist 50% or more in the marginal area to be potential-defined or in the expanded marginal area to be potential-defined.
It is also preferable that the electrode be provided on a second plate opposed to the first plate and that the electrode be provided in a range extended by at least the distance 2xcex1d (where xcex1 is a value not less than 0.6 and not more than 1) in all directions parallel to the second plate from the edge of an irradiated area which electrons emitted from the electron-emitting device irradiate.
At least part of the potential defining region may be comprised of an electroconductive plate placed between the first plate and the electrode.
The potential defining region may be provided in contact with the first plate or spaced away therefrom. When spaced away, it can be provided as an electroconductive plate. The potential defining region can be provided as an additional control electrode such as the grid electrode or the like, different from the electrode.
Each of the invention described above can be particularly suitably applicable to the structure with a plurality of above-stated electron-emitting devices. Particularly, the invention is suitable for the structure in which the plurality of electron-emitting devices are arranged in a matrix pattern. A suitably applicable configuration is such that a plurality of electron-emitting devices are arranged in a matrix pattern and the plurality of devices are wired in the matrix pattern with a plurality of row-directional wires and a plurality of column-directional wires provided approximately along a direction perpendicular to the row-directional wires.
The cold-cathode emission devices can suitably be adopted as the electron-emitting devices. Particularly, the field emission type and surface conduction electron-emitting devices can be suitably used.
The present application also includes the invention of the image-forming apparatus comprising the above-stated electron beam emitting apparatus and the phosphor emitting light under irradiation of electrons emitted from the electron-emitting device of the electron beam emitting apparatus, as the invention of the image-forming apparatus.